Moscow and Washington had long accused each other of breaching its terms, and President Donald Trump formally pulled the US out last November.

Trump's administration said the Kremlin had "weaponised" the treaty to target "critical infrastructure" in the US and Europe and prevented American flights over its exclave Kaliningrad.

The US withdrawal came despite the dismay of Washington's European allies, who remain attached to the treaty as part of their continent's security architecture.

Now Moscow has announced it is pulling out as well after a "lack of progress" in keeping the treaty functioning following the US decision to quit.

The Russian foreign ministry said Friday that the United States had used a "fictitious pretext" for its withdrawal and in doing so disturbed "the balance of interests of the participating states".

It said Russia had put forward proposals to retain the "viability" of the treaty but did not receive support from Washington.

During Trump's tenure the United States withdrew from two major international accords -- the Iran nuclear deal and the Open Skies treaty -- and pulled out of a centrepiece arms control agreement with Russia, the Intermediate-Range Nuclear Forces (INF) treaty.

- Observation -

The Open Skies Treaty made it possible to conduct joint unarmed observation flights over the territories and to take images using sensors of a predefined resolution.

It also allowed signatories to request copies of all images taken during overflights carried out by others.

Overflights have been governed by quotas, negotiated annually and assigned to specific aircraft. The United States, for example, was allowed to operate Boeing OC-135 planes with infrared scanners.

The country under surveillance has been given 72 hours' warning of a flight and 24 hours notice of the route, to which it can suggest modifications.

The treaty laid down which air bases can be used for the flights and at which points they can cross into each other's air space. Russia and the US had four such bases each.

A committee to oversee the implementation of the treaty came together in Vienna every month at the headquarters of the Organisation of Security and Cooperation (OSCE) in Europe.

"Its unique feature consists in the fact that during overflights, representatives of both the observing state and the observed state can sit together in one aircraft," said Alexander Grief and Moritz Kutt, researchers at the Institute for Peace Research and Security Policy in Hamburg, in a report.

They warned the US withdrawal would be an important loss for its NATO allies in Europe as most of them did not possess satellite reconnaissance capabilities.

Beyond the US and Russia -- the remaining signatories of the treaty are Belarus, Belgium, Bosnia and Herzegovina, Bulgaria, Canada, Croatia, Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Turkey, Ukraine, United Kingdom. Kyrgyzstan has signed, but not ratified the treaty.

csg/del/pma

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